Exhaust, from my experience, doesn't matter in size. As long as it's big enough to efficiently evacuate the gasses after the header. That is where the power is gained or lost. 3" exhaust will work, but is over-sized. Which is not a problem at all except for the added weight and space hogging and ground clearance.. The glass pack belongs on redneck trucks and hot rods. It has no place on a Honda. It'll sound raspy and ricey and like general crap. That being said, the high flow cat and 3" stainless piping should be solid stuff. Throw a decent muffler on it and call it a day. Assuming you are getting a really good deal on it. If it's expensive, pass.